In recent years, micromachining technology and ultra microfabrication technology have made it possible to develop a one-chip system where conventional apparatuses or means (e.g., pump, valve, flow path and sensor) for sample preparation, chemical analysis and chemical synthesis are formed into a microstructure (Patent Document 1) This system is also called the μ-TAS (Micro Total Analysis System) bioreactor, lab-on-chips or biochip. The application of this system is anticipated to bring about a great success in the field of medical inspection, diagnostic field, environmental measuring field, and agricultural production field. In practice, as can be observed in genetic screening, when a complicated process, skilled manipulation and operation of instruments are required, an automated and simplified high-speed micro-analysis system can be said to bring about huge benefits of the required cost, amount of samples and time as well as no restriction of time and place of analysis.
In various forms of analysis and inspection, the chip for analysis is required to provide superb quantitative property, accuracy and economy in analysis. To achieve these objects, it is important to establish a liquid feed system characterized by a simple structure and high reliability. Thus, there has been an intense demand for a micro-fluid control elements characterized by a high degree of accuracy and reliability. The present inventors have already proposed a micro-pump system and its control method preferably used to achieve these objects (Patent Documents 2 through 4).
The aforementioned analysis chip is preferred to permit reaction between a sample and a mixed reagent prepared by mixing a plurality of reagents. However, such a so-called micro-reactor requires that various forms of mixing operation such as mixing between reagents, mixing between a reagent and sample are performed within a single chip. This requires a high degree of accuracy in the feed of reagents and others, as exemplified by exact timing for confluence with various reagents and others, and feeding of reagents and others under a predetermined pressure. Failure of high-precision feed of the reagents and others will lead to adverse effect upon reaction and result of detection.
In the meantime, as a mechanism for feeding a trace quantity of liquid in the minute flow path in the aforementioned analysis chip, a various kinds of methods such as a method based on differences in pressure of gases have been proposed. However, in the drive operation based on the principle of pressure difference based on suction and pressurization wherein a gas of predetermined pressure is used as a driving force, the stability of liquid feed tends to be disturbed by expansion and shrinkage of the gas when there are temperature differences in various regions within a flow path. Another problem is that, if there is a mechanism where a great pressure loss is caused in the middle of the flow path, there is a big change in flow rate before and after the passage of liquid through the portion where the great pressure loss is caused.
On the other hand, a liquid feed method for micro-fluid device is disclosed, where by using an oily driving solution, an aqueous solution incompatible with the oily solution is pushed downstream, whereby the liquid is fed (Patent Document 5).
However, the aforementioned problems can be caused when air bubbles are present between these liquids. For example, if the solution to be fed is put into the minute flow path of an analysis chip, and a driving solution is poured thereafter from the upstream thereof through the inlet of the chip via a pipe or the like, air bubbles are often present between these liquids.    Patent Document 1: Unexamined Japanese Patent Application Publication No. 2004-28589    Patent Document 2: Unexamined Japanese Patent Application Publication No. 2001-322099    Patent Document 3: Unexamined Japanese Patent Application Publication No 2004-108235    Patent Document 4: Unexamined Japanese Patent Application Publication No. 2004-270537    Patent Document 5: Unexamined Japanese Patent Application Publication No. 2004-61320